The electrical wires and cables of most commercial and industrial installations are encased within a rigid protective sheath or conduit. In such installations the conduit is generally installed first by laying it out and extending it along predetermined paths from an inlet power source station to outlet junction or power distribution boxes or plugs. Such conduit paths can be very diverse, extending within and through walls, ceilings and floors, and around numerous bends and angles. Similarly, modern day telephone and electric power distribution lines are now typically encased within rigid conduits buried deep within the ground and often extending for thousands of feet between access ports or terminals.
Electrical cables or wires are then installed within the empty conduits by first feeding or pushing a semi-rigid/flexible pull strand commonly referred to as a fishtape, through the conduit, from its inlet source to an outlet box or distribution terminal. The trailing end of the pull strand or fishtape is then secured to one end of the electrical cable(s) to be pulled through the conduit, and the leading end of the pull strand or fishtape is manually or mechanically pulled so as to advance the electrical cable(s) through the conduit. In large conduit installations, wherein a number of thick electrical cables are to be pulled through the conduit, the pull strand typically comprises a multi-strand steel cable or polyester fiber rope capable of withstanding thousands of pounds of pulling tension. Such pull strand winch lines are typically connected to large pulling winches mounted adjacent the conduit outlet.
Whether the application is related to a small electrical contractor pulling wires within one-half inch or one inch conduits for residential or commercial buildings, to a telephone company pulling hundreds of wires through 31/2 inch diameter conduits extending over 1,000 foot runs, or to a large commercial contractor pulling large power cables through 5 inch conduits in a nuclear power plant installation, the problems associated with such electrical cable or wire pulling through conduits are universal throughout the electrical industry. The frictional drag forces created between the outer walls of the electrical cables being pulled and the inner surface of the conduit through which they are being pulled, creates a pulling "tension" in the electrical wire that defines the limits on the length of any single pull and the total angle of bends through which the cable may be pulled. The pulling tension created by pulling a wire through a straight conduit segment is generally linearly proportional to the coefficient of friction between the wire and conduit, and the length of the conduit segment. However, the pulling tension forces required to pull the same wire through a bend in the conduit, increase exponentially. Therefore, every bend in the conduit through which the electrical cables must be pulled significantly increases the pulling tension forces applied to the wire and places severe limitations on the entire process. To further complicate matters, crude conduit bending techniques that often exist in smaller installations may result in distortions to the cross-sectional shape of the conduit at a bend radius, causing a restrictive cross-sectional area through which the cable must pass, exactly at that point in the conduit run which already significantly contributes to higher pulling tension forces. In larger conduit installations (e.g. 5 inch conduits), it is not uncommon to experience pulling tension forces of several thousand pounds.
It is obviously desirable to minimize such tension forces that are exerted on the electrical cables and wires during a pulling operation. Severe pulling tension forces can be damaging to the electrical wire in several respects. Industry standards specify the maximum "sidewall" stress that can be applied to an electrical cable during a pulling operation, before damage to the protective coating or insulation of the wire will ensue. When pulling wires of smaller diameter, excessive pulling tension can actually result in stretching of the wire, unevenly reducing the wire diameter at the stretch point, increasing the electrical resistance of the wire and causing unsafe hot spots in the wire at those locations. In large installations, tension pulling forces are often monitored with a dynamometer to insure that the maximum pulling tension specifications are not being exceeded. The consequences of a cable getting "stuck" within a conduit are generally catastrophic. Occasionally, the lodging forces are so extreme that the cable cannot be dislodged by pulling it backward through the conduit. In some instances, the entire conduit run must generally be removed or dug up if buried. In the case of a nuclear power plant, for example, wherein the conduits are permanently embedded within many feet of concrete, a stuck cable can be extremely costly.
To reduce the pulling tension forces required to pull electrical cables through a conduit, lubricants have been applied to the electrical wires as they enter the conduit. Such lubricants have typically been either in the form of a slippery gel or of a pourable nature. The simplest technique for applying the lubricant to the electrical cable is often performed manually by a person simply smearing the lubricant gel onto the cable(s) as it enters the conduit. More comples and costly techniques such as disclosed in U.S. Pat. No. 4,296,837 to Charlton, that sprays a lubricant onto the progressing cable from a collar mounted at the inlet of the conduit, have also been devised. Such techniques, however, are generally too costly and complex to be practical to the contractor who must deal with diverse conduit sizes and environmental obstacles which preclude the use of such complex equipment. Frequently, such direct application to the electrical cable(s) is not adequate when used by itself for cable pulls of extended lengths or for those conduits having multiple bends. Most of the lubricant applied to the cables is deposited on the inner walls of the conduit near the inlet to the conduit, and little lubricant remains on the cable surface where it is most needed, at a location further down the conduit, and at bends in the conduit.
Accordingly, a number of structures and techniques have been devised for "distributing" lubricant along the length of the conduit as the electrical cable(s) is being pulled through the conduit. In general such prior art techniques have not provided an optimum balance between cost, simplicity and practicality. Effective, metered application of the lubricant along the conduit in a manner that selectively and reliably deposits more lubricant at those portions of the bends in the conduit where such lubricant is most needed has long been desired in the industry. While the greatest pulling tension-contributing force at a bend in a conduit is derived from engagement between the cable and that conduit wall defining the inner radius of the bend, most prior art lubricant spreaders fail to adequately or consistently apply metered amounts of lubricant to such inner radius conduit wall, thus failing to apply the lubricant where it is essentially needed. Further, the prior art conduit lubricant spreader devices generally do not provide for precise metered application of the lubricant to the conduit so that precise amounts of lubricant can be inserted within the conduit in advance of the spreader so as to minimize lubricant waste, or alternatively, do not have the practical capacity for holding a sufficient amount of lubricant required for lubricating the entire conduit run. By way of example only, several prior art techniques that have been devised for lubricating the inside surfaces of conduit runs will be briefly described below.
U.S. Pat. No. 3,858,687 to Masarky et al, discloses a technique wherein thin, rupturable, lubricant-containing packets are adhesively secured to the pull-strand winch line in advance of the electrical cable. As the pulling cable frictionally engages the conduit sidewalls at conduit bends the increased pressure applied to the packets will cause them to rupture, thus dispensing their contents. This technique allows for little if any application of lubricant along straight conduit runs and does not uniformly and reliably lubricate all bends along the conduit. As a practical matter most of the packets would be ruptured and dispense their contents at the first conduit bend, leaving no lubrication for subsequent bends.
U.S. Pat. No. 4,108,279 to Marcell, discloses a lubricant "dispensing" device that holds the lubricant, and which is positioned in advance of the electrical cable being pulled through the conduit. The dispenser uses a piston assembly for ejecting lubricant out of an opening in the forward end of the dispenser. The device attempts to dispense more lubricant to the conduit in areas where the pulling tension is greatest. The structure is generally complex and impractical for commercial use, it being generally impractical for long conduit run applications due to its limited lubricant reservoir size. Further, since the device is responsive to pulling tension, which generally continually increases with the length of electrical cable within the conduit, the device will have a tendency to deposit proportionately "more" lubricant as it progresses down the conduit, regardless of the number of bends it traverses along the way. Furthermore, the device does not insure application of lubricant to that conduit wall defining the "inner" radius of a bend, but would appear to deposit more lubricant to that conduit wall defining the "outer" radius of the curve (i.e. where the lubricant is least needed).
U.S. Pat. Nos. 4,137,623 and 4,275,096 to Taylor, describe cartridge-type dispensers having lubricant impregnated porous material compressibly packed between an inner sleeve casing and a carrier. As pulling tension is applied to the cartridge via the pulling strand or cable, the absorbent material expands to engage the inner diameter of the conduit, applying lubricant coating to the walls of the conduit. This type of lubrication structure is generally too complex and expensive to be commercially practical, has potentional reliability problems due to the number of moving parts involved for its operation, does not lend itself to large commercial application due to its small lubricant reservoir and does not effectively provide for increased lubrication at the conduit bends, as previously discussed.
U.S. Pat. No. 3,595,636 to Honeycutt, Jr., while not a lubricating device per se, describes an applicator for applying a protective coating to the inside surface of a generally straight, short section of pipe. The applicator has an exterior surface having longitudinal grooves and has generally flexible sidewalls to accommodate imperfections in the pipe. The device is not intended for use in cable pulling operations but is "pushed" through the pipe with compressed air or gas forced through the pipe from behind the applicator. This type of structure would generally be ineffective as an applicator for electrical cable pulling operations and would be ineffective for selectively applying more lubrication at bends in the conduit, as discussed above.
U.S. Pat. No. 4,296,837, previously referenced, in addition to the collar assembly for lubricating the electrical cable itself, also discloses a spray lubrication device that preceeds the electrical cable through the conduit. The spray device is supplied with lubricant fluid through a hose which extends from the exit of the conduit, the entire length of the conduit. This type of pump system is generally impractical for use by the average electrical contractor, is cumbersome to use due to the necessity of the long supply hose and supply pumps and does not automatically provide for selective additional lubrication to the conduit at the locus of its bends.
A simple prior art spreading structure that has been used for metering and applying a lubricant gel to the inside of the conduit has been a cylindrical rubber grommet having an outer diameter generally equal to that of the inner diameter of the conduit, and having a plurality of longitudinally peripherally extending grooves. The pulling cable passes through an axially aligned hole in the grommet, and the grommet is pulled along with the pulling cable through the conduit. A mass of lubricant is deposited within the conduit immediately preceeding the grommet, which pushes the lubricant before it through the conduit and applies the lubricant to the inner walls of the conduit as the lubricant passes through the outer grooves of the grommet. While this device is generally effective for metered lubrication of "straight" conduit runs, it does not effectively apply lubricant at the bends of the conduit. As the pulling cable progresses around a bend in the conduit, the cylindrical grommet is deformed under the pulling tension (in the radial direction) of the pulling cable, causing the grommet to actually wipe lubricant from that portion of the conduit forming the inner radius of the bend (i.e. where the lubricant is needed most) and causing it to apply excess amounts of lubricant to that portion of the conduit forming the outer radius of the bend (i.e. where the lubricant is least needed).
Therefore, while the electrical cable pulling industry has recognized the need for an effective spreading device for distributing lubricant within a conduit, and while the prior art structures developed to handle the problem have gone to great pains in developing intricate, complex and expensive assemblies for dealing with the situation, no single device has provided a simple, effective, reliable solution that can provide both adequate material distribution over long conduit runs and that can accurately and reliably deposit additional quantities of lubricant to the inside (or shorter) radius surface of the conduit at and just before bends in the conduit, where such lubricant is most needed. The present invention provides a simple, cost-effective method and apparatus that solves the above-described shortcomings of prior art lubricant spreading techniques and structures. The lubricant spreader of this invention is simple to use and is of rugged construction, involving no intricate moving parts, provides for positive and uniform metered application of lubricant along straight runs of conduit and consistently applies additional lubricant, exactly where the lubricant is most needed, to the inner (shorter) radius wall of the conduit at and just before a bend in the conduit. Due to its reliable metering property, the present invention allows the user to accurately determine the precise amount of lubricant that will be needed for any particular cable pulling project, preventing waste of the lubricant and undue clean-up of excess lubricant at the conduit outlet port.